1. Field of the Invention
The present invention relates to electrical direct current systems with batteries, which find application for the storage and delivery of electrical energy in the most diverse applications, for instance in land, air or water vehicles, especially as auxiliary energy sources for starting a main motor, or as storage elements in USV (uninterruptible power supply) installations, solar installations or wind generator installations, according to the preamble to claim 1.
2. History of Related Art
The invention is further described below in the example of rechargeable batteries, to which belong especially the lead-acid batteries common in automobiles, and also the well known NiCd elements, without the invention being restricted to these two types of battery.
The power capability of a battery of the type quoted is, for a given nominal capacity, chiefly dependent on its charge condition, the type and number of the previous charging cycles and strongly on its operating temperature. In ground conveyor vehicles, for instance fork lift trucks, and in sailing boats, the recharging of the battery is required in the shortest possible charging cycles and at the maximum charging current. In order not to shorten the lifetime of the battery, the so-called gas potential must not be exceeded. The optimum charging can only be performed in dependency on the actual battery temperature. If for instance the discharged battery is charged by too high a current in too short a time in the cold condition, its lifetime as well as its energy storing capacity is diminished. If the battery is put into service after a long interruption, as a rule neither its charge condition nor its available total capacity is known. This is a disadvantage, since in ignorance of these data a battery which is no longer sufficiently capable of performance may not be exchanged or exchanged too late.
Both in the charging and also the discharging of the battery, as well as the temperature, the currents flowing, the available terminal voltage, the instantaneous electrical power and the overall available energy are of interest: in the discharging of a battery, for instance too great a current, an unexpectedly large output, an unusually low terminal voltage or an increased temperature are indications of a short circuit. During charging a damaging overcharging can be concluded from an increased temperature.
The determination of these physical values, given as examples, which concern the battery, and their presentation on one or more indicating elements do not of themselves present any problem in principle. A considerable expense is required for this however, since for each of the values of interest, such as for instance the temperature, the current flow or the terminal voltage, an individual sensor is required. Each of these sensors must as a rule have access to its own power supply. In conventional, analog measuring systems each sensor output requires its own transmission line to the display unit. The conversion of the sensor signals into a computer conforming form, for instance in a digital presentation, the processing of this data in a computer and the transmission with the aid of the computer of determined physical values is associated with further expense, and in each case a minimum two wire data line, often of considerable length must be installed between the battery and the display unit.